This invention relates to treatment of a waste gas containing fluorine-containing compounds. More particularly, it relates to a method and an apparatus for efficient treatment of emissions from semiconductor fabrication plants, particularly from steps of dry cleaning an inner surface of a fabrication apparatus and etching various kinds of deposited films with perfluorocarbons (PFCs) and halogenated hydrocarbons such as C2F6, C3F8, CHF3, SF6 and NF3. The waste gases contain not only PFCs but also oxidizing gases such as F2, Cl2 and Br2, acidic gases such as HF, HCl, HBr, SiF4, SiCl4, SiBr4 and COF2, as well as CO.
Semiconductor fabrication plants use many kinds of harmful gases that can potentially pollute the environment. PFCs contained in waste gases that typically result from etching and CVD steps are suspected of causing global warming, and it is urgently needed to establish an effective system for their removal.
Various breaking and recovery techniques have heretofore been proposed for PFC removal. Catalytic thermal decomposition is one of the breaking techniques and uses versatile compounds such as Pt catalyst, zeolite-based catalysts, activated charcoal, activated alumina, alkali metals, alkaline earth metals and metal oxides. However, none of these catalytic compounds have proved completely satisfactory.
Waste gases discharged from a semiconductor fabrication process contain not only PFCs, but also oxidizing gases such as F2, Cl2 and Br2, acidic gases such as HF, HCl, HBr, SiF4, SiCl4, SiBr4 and COF2, as well as CO; however, no method has yet been established that can realize a thorough and effective treatment of these harmful gases.
If one wants to treat oxidizing gases such as F2, Cl2 and Br2 by a wet method, thorough treatment cannot be achieved by use of water alone. If alkali agents or reducing agents are also used, not only process control but also a treatment apparatus becomes complicated and, in addition, cost of treatment increases.
To remove CO, it has to be decomposed with oxidizers such as those based on Cu or Mn. As for PFCs, it has been proposed to use alumina as an agent for removing them (Japanese Patent Public Disclosure No. 286434/1998), and this method is characterized by contacting C2F6 with molecular oxygen. However, the lifetime of alumina is very short and throughput or an amount of C2F6 that can be treated for 100% decomposition is only 4.8 L/L. Additionally, no effective way has been proposed to deal with CO that occurs as a by-product of C2F6 decomposition, and oxidizing gases and acidic gases that occur concomitantly with PFCs.